1. Field of the Invention
The present invention relates to a wideband (DC to GHz) PC-board Balun. This wideband balun is suitable for use in communication systems, radars, radio frequency transmitters, receivers, signal processors, and more specifically to ultra wide band width (UWB) applications such as impulse radar. The word "balun" was derived by joining the words "balanced" and "unbalanced" together, since it is the function of a balun to connect a balanced electrical network to an unbalanced electrical network. A balanced network is one where no ground currents flow and instead, there is a "plus" wire and a "minus" wire that counteract or balance each other.
2. Description of the Prior Art
A great variety of baluns are available commercially that cover a broad spectrum in terms of size, bandwidth, center frequency, and insertion loss. However, these commercial baluns do not have the wide bandwidth, balance, insertion loss, or power handling capability required for ultra wide bandwidth applications such as impulse radar. Impulse radar is presently being used in a variety of radar systems to detect aircraft, ground vehicles, people, mines, buried pipes, roadway faults, buried homicide victims, tunnels, leaking buried pipes, and similar items. Consequently, it is desirable to have a balun that maintains low insertion loss and good balance for UWB applications. Accordingly, it is an object of this invention to provide a balun that maintains low insertion loss and good balance for UWB applications.
A recent example of a wide bandwidth balun is shown in U.S. Pat. No. 5,172,082 to Livingston et al. This balun uses microstrip conductors on a printed circuit board to achieve a wide bandwidth. This design, however, requires external circuitry to achieve the phase inversion required by the balun. In addition, the balanced output does not have the field of the two lines aligned in a manner suitable for end launch applications such as feeding a horn antenna. This design also only provides a means for dividing the unbalanced signal into two transmission lines which only allows the balun to have a 4:1 impedance ratio. It does not provide a method for creating a greater impedance ratio as required in some applications. In addition, the operational bandwidth of the previous balun design does not extend down to DC (direct current).